Arrangement for guiding expired respiratory gas flow

ABSTRACT

An arrangement and method for guiding expired gas flow in a breathing circuit through a housing assembly for removing an undesired gas component is disclosed herein. The housing assembly includes a first port and a second port, one of the ports receiving the flow and another discharging the flow. The arrangement includes a gas routing device in flow communication with the breathing circuit and the housing assembly. The routing device is provided with at least two different route options. According to a first option the gas is guided to the first port and through the housing assembly to the second port and to the gas routing device for guiding for the inspiration. According to a second option the gas is guided to the second port and through the housing assembly to the first port and to the gas routing device for guiding for the inspiration.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/459,339, filed Apr. 30, 2012, entitled “Arrangement and Method forGuiding Expired Respiratory Gas Flow Using Gas Routing Device,” which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The disclosure relates generally to an arrangement and method forguiding expired respiratory gas flow in a breathing circuit through ahousing assembly for removing an undesired expired gas component of therespiratory gas flow before conveying for an inspiration of a subject.The housing assembly comprises a first port and a second port, one ofthe ports being for receiving the gas flow and another of the portsbeing for discharging the gas flow. The disclosure also relates to abreathing circuit for ventilating lungs of a subject.

Anesthesia machines are optimized for delivering anesthesia to a patientusing volatile anesthetic agent liquids. In such systems, the anestheticagent is vaporized and mixed into the breathing gas stream in acontrolled manner to provide a gas mixture for anesthetizing the patientfor a surgical operation. The most common volatile anesthetic agents arehalogenated hydrocarbon chains, such as halothane, enflurane,isoflurane, sevoflurane and desflurane. Additionally, nitrous oxide(N₂O) can be counted in this group of volatile anesthetic agents,although the high vapor pressure of nitrous oxide causes nitrous oxideto vaporize spontaneously in the high pressure gas cylinder, wherefromit can be directly mixed as gas with oxygen. The anesthetizing potencyof nitrous oxide alone is seldom enough to anesthetize a patient andtherefore another volatile agent is used to support that.

Since the volatile anesthetic agents are expensive, they are effectivegreenhouse gases and further harmful to the atmospheric ozone layer,anesthesia machines have been developed to minimize the consumption ofthe gases. To keep patients anesthetized, a defined brain partialpressure for the anesthetic agent is required. This partial pressure ismaintained by keeping the anesthetic agent partial pressure in the lungsadequate. During a steady state, the lung and body partial pressures areequal, and no net exchange of the anesthetic agent occurs between theblood and the lungs. However, to provide oxygen and eliminate carbondioxide, continuous lung ventilation is required.

Anesthesia machines are designed to provide oxygen to the patient andeliminate carbon dioxide (CO2), while preserving the anesthetic gases.To meet these goals a re-breathing circuit is used. In this patientexhaled gas is reintroduced for inhalation. Before re-inhalation carbondioxide must be removed from the gas, which is done with a carbondioxide absorber. Before inhalation, the gas is supplied with additionaloxygen and anesthetic agents based upon the patient demand. In thisarrangement, the additional gas flow added to the re-breathing circuitcan be less than 0.5 L/min although the patient ventilation may be 5-10L/min. Such ventilation of the lung is carried out using a ventilatorpushing inhalation gas with overpressure to patient lungs and thenallowing that to flow out passively from the pressurized lungs to thebreathing circuit.

Ventilation carries the breathing circuit oxygen to lungs for uptake tobe burned in body metabolism. The outcome of this is CO2 that bloodcirculation transports to lungs wherefrom it becomes carried out withexhalation gas. Before re-inhalation the gas is guided through absorberfor CO2 removal. Effective CO2 removal requires close contact with thebreathing gas and the removing substance. To provide large contact area,the removing substance is therefore a surface of porous structure ofgranules that fill the cartridge. The form of this granular structure isguided by the flow resistance, the limitation of which is one key designgoals of the breathing circuit. In absorber optimized for minimalresistance the gas flow path through the stacked granules is short andthe flow distributes to wide area. In such structure the gas flowsslowly because of large surface area providing time for reaction betweenthe gas and absorbent granules.

Absorber canisters have two gas connections: One inlet for the gas flowcarrying carbon-dioxide and one outlet. Between inlet and outlet thecanister has a gas pathway. The absorber granules form part of thispathway during which the carbon dioxide is removed from the gas.

The CO2 absorption is based on chemical reaction in the absorptioncartridge. Typically the reaction is based on the use of alkalinechemicals often referred as soda lime (mainly including calciumhydroxide) that react with aqueous CO2. Typical end results of thisexothermic reaction are calcium carbonate and water. The air exhaled bythe patient includes approximately 5% of CO2. A fresh absorber is ableto purify the breathing air from CO2 virtually completely. When theabsorption capacity is getting exhausted there is a gradual increase ofCO2 in the air downstream the absorber. A typical clinical practice isthat latest when the inspiratory air reaches CO2 content of 0.5% theabsorber unit needs to be replaced.

The CO2 absorption takes place in the soda lime bed inside the absorbercartridge. Depending on the absorber, such as container geometry,absorbent chemistry and grain characteristics, and the clinical factors,such as the amount of exhaled CO2, respiratory rate, etc, as well as theanesthesia machine set ups, such as used fresh gas flow, the absorbentvolume and specifically the absorbent bed height required for completeCO2 removal change. This height or zone in the absorbent bed requiredfor appropriate absorption of CO2 is often referred as “mass transferzone”. Due to the characteristics of the absorption reaction andspecifically the mass transfer zone a single absorber unit alwaysincludes a remarkable amount of unused absorbent at the time when itneeds to be replaced to maintain below 0.5% CO2 levels since therequired mass transfer zone at that moment is bigger than there is freshabsorbent remaining.

The problems related to the inability to fully use a single absorber donot exist in all anesthesia machine designs, in case there are twoidentical absorber units on top of each other. The absorbers are notintended to be replaced simultaneously but individually only after theindividual absorber is fully exhausted. In practice this is accomplishedby having the more exhausted absorber being exposed to the CO2 rich gasfirst. Even when it reaches the point where it has not enough capacityto absorb all the CO2 the second more fresh unit downstream is stillcapable of absorbing the remaining CO2. When the first absorber is fullyexhausted it should be removed and the other partially used absorber canbe mounted to the place where the first absorber used to be and a newfresh absorber is placed to the spot where the second absorber used tobe. And the absorber changing cycle starts over again. On the other handthere are some concerns that the benefits of a twin absorber design maynot be fully exploited if it is not easy or intuitive enough how tomanage the swapping of the absorber units. Specifically, how to makesecure the right absorber unit is moved from one port to another andthat the right unit replaced with a new one.

However, there are some benefits with the more recently developed singleabsorber designs over the twin absorber assembly. One of them is thefact that in the single absorber designs available in the market placethe gas return path is integrated into the absorber assembly and hencethey require no additional conduit for return gas. In the well-knowntwin absorber design the gas return conduit is a part of the anesthesiamachine—not integrated into the absorber. This means that even if a caregiver uses disposable twin absorbers that are not serviced but simplydisposed after use there still is the gas return conduit in theanesthesia machine that needs cleaning to avoid cross contamination.Also, all the parts in the breathing circuit add up the total airvolume. However, a minimized air volume is preferable. The benefitsinclude smaller total amount of anesthetic agents required as well assmaller system gas compliance.

BRIEF DESCRIPTION OF THE INVENTION

The above-mentioned shortcomings, disadvantages and problems areaddressed herein which will be understood by reading and understandingthe following specification.

In an embodiment, an arrangement for guiding expired respiratory gasflow in a breathing circuit through a housing assembly for removing anundesired expired gas component of the respiratory gas flow beforeguiding for an inspiration of a subject, the housing assembly having afirst port and a second port, one of the ports being for receiving thegas flow and another of the ports being for discharging the gas flow,includes a gas routing device in flow communication with the breathingcircuit and the housing assembly through the first port and the secondport. The routing device is provided with at least two different routeoptions, a first route option is configured to guide the expired gasfirst to the first port of the housing assembly and through the housingassembly to the second port of the housing assembly and to the gasrouting device for guiding along the breathing circuit for theinspiration, a second route option is configured to guide the expiredgas first to the second port of the housing assembly and through thehousing assembly to the first port of the housing assembly and to thegas routing device for guiding along the breathing circuit for theinspiration.

In another embodiment, a breathing circuit for ventilating lungs of asubject includes a first limb for guiding expired respiratory gas, and ahousing assembly having a first port and a second port, one of the portsbeing for receiving the expired gas flow and another of the ports beingfor discharging the gas flow, the ports allowing the expired respiratorygas flow through the housing assembly to remove an undesired expired gascomponent of the respiratory gas flow. The breathing circuit forventilating lungs of a subject also includes a second limb for guidingthe respiratory gas received from the housing assembly for aninspiration, and an arrangement for guiding expired respiratory gas flowthrough the housing assembly before conveying for an inspiration. Thearrangement comprising a gas routing device in flow communication withthe first limb, the second limb and the housing assembly through thefirst port and the second port, the routing device being provided withat least two different route options, a first route option beingconfigured to guide the expired gas first to the first port of thehousing assembly and through the housing assembly to the second port ofthe housing assembly and to the gas routing device for guiding along thesecond limb for the inspiration, a second route option being configuredto guide the expired gas first to the second port of the housingassembly and through the housing assembly to the first port of thehousing assembly and to the gas routing device for guiding along thesecond limb for the inspiration.

In yet another embodiment, a method for guiding expired respiratory gasflow in a breathing circuit through a housing assembly for removing anundesired expired gas component of the respiratory gas flow beforeguiding for an inspiration of a subject, the housing assembly having afirst port and a second port, one of the ports being for receiving thegas flow and another of the ports being for discharging the gas flow,includes choosing from at least two different route options the expiredrespiratory gas flow through the housing assembly. A first route optionis configured to guide the expired gas first to the first port of thehousing assembly and through the housing assembly to the second port forguiding along the breathing circuit for the inspiration. A second routeoption is configured to guide the expired gas first to the second portof the housing assembly and through the housing assembly to the firstport of the housing assembly for guiding along the breathing circuit forthe inspiration.

Various other features, objects, and advantages of the invention will bemade apparent to those skilled in art from the accompanying drawings anddetailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a breathing circuit for ventilatinglungs of a subject;

FIG. 2 shows a schematic cross-sectional view of an arrangement forguiding expired respiratory gas flow through a housing assembly forremoving an undesired respiratory gas component in accordance with anembodiment; and

FIG. 3 shows a schematic cross-sectional view of an arrangement forconveying expired respiratory gas flow through a housing assembly forremoving an undesired respiratory gas component in accordance withanother embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments are explained in the following detailed descriptionmaking a reference to accompanying drawings. These detailed embodimentscan naturally be modified and should not limit the scope of theinvention as set forth in the claims.

In FIG. 1 a breathing circuit 1 for ventilating lungs 2 of a subject isdisclosed. The breathing circuit comprises a ventilator 3 supplyingalong a ventilator connection 4, such as a ventilator tube, breathinggas to the lungs for an inspiration and receiving breathing gas forexpiration. The ventilator may be whichever well-known type e.g. drivegas based pneumatic flow-valve or mechanical piston driven. Also thebreathing circuit comprises a gas mixer 5 supplying a fresh gas in thisspecific embodiment along a fresh gas tube 6 for the subject breathing.The gas mixer may comprise an anesthetic agent supply (not shown in theFigure) such as an anesthetic agent vaporizer providing anesthetic agentfor the subject breathing.

The breathing circuit 1, which may be a re-breathing circuit, comprisesalso a first limb 8, such as an expiration limb, discharging anexpiration gas and a second limb 9, such as an inspiration limb,providing an inspiration gas including the fresh gas for the subjectbreathing. Thus the first limb 8 and the second limb 9 connect lungs ofthe subject to the ventilator 3 and the gas mixer 5. The ventilator 3 iscontrolling the breathing circuit pressure through the ventilatorconnection 4. Also the breathing circuit comprises a housing assembly 10for removing, such as absorbing, an undesired respiratory gas componentof a respiratory gas flow before conveying along the second limb 9 foran inspiration. The housing assembly 10 may comprise only one housingbut advantageously as shown in FIG. 2 at least two housings which may bedetachable from the breathing circuit and which are a first housing 17and a second housing 18 in flow communication with each other forremoving an undesired expired gas component of the respiratory gas flowbefore conveying along the second limb for the inspiration.

The housings of the housing assembly may include a substance, which maybe solid fluidal material, such as granules for removing an undesiredrespiratory gas component of a respiratory gas flow. Typical substanceused in anesthesia is a carbon dioxide absorbing material, which may besoda-lime, a mixture of calcium hydroxide, sodium hydroxide, potassiumhydroxide and water or any other substance that can extract CO2 from gasmixture e.g. molecular sieve or amines. The material may chemicallyreact with carbon dioxide or otherwise remove it from the breathing gas.

Typically the breathing circuit 1 also comprises directional valves 11and 12 guiding the gas flow in the circuit on direction indicated byarrows 13. For inhalation the ventilator 3 increases the breathingcircuit pressure by adding the gas flow from ventilator connection 4.Directional valves 11 and 12 guide the gas flow through the housingassembly 10 to remove in this embodiment carbon dioxide from thebreathing gas, to the second limb 9 and further along a subject limb 14to the subject's lungs 2. For expiration the ventilator 3 releases gasesfrom the breathing circuit through the ventilator connection 4. For thispurpose the ventilator 3 may e.g. operate an expiration valve (not shownin Figure). This will allow the gas flow from distended subject's lungsthrough the subject limb 14 to the first limb 8 and further through thedirectional valve 12 to the ventilator connection 4. The directionalvalve 11 prevents the gas flow from the subject's lungs to enter thesecond limb 9 hereby maintaining the second limb free from CO2. Instead,the exhaled gas is rich of CO2 that needs to be removed before beingre-circulated for the inspiration, which is done in the housing assembly10 including the substance removing carbon dioxide.

The breathing circuit 1 further comprises an arrangement 20 shown moredetailed in FIG. 2 for guiding expired respiratory gas flow arrivedalong the first limb 8 through the housing assembly 10. The arrangement20 may comprise, if desired, a first gas connection 26, such as achannel, and a second gas connection 27, such as a channel, for guidingthe respiratory gas flow arrived along the first limb 8 towards thehousing assembly 10 and from the housing assembly along the second limb9 for the subject breathing. Thus one of the first and second gasconnections is configured to guide the respiratory gas received alongthe first limb 8 towards the housing assembly 10 and another one or inthis case the remaining one of the first and second gas connections isconfigured to convey the respiratory gas from the housing assembly 10along the second limb 9 for the subject breathing.

The arrangement 20 comprises a gas routing device 30, such as adirectional valve, for guiding the flow direction, which valve is inflow communication with the first gas connection 26 and the second gasconnection 27, if such connections are desirable. The gas routing device30 as well as the housing assembly 10 through the gas routing devicetypically is in flow communication with the second limb 9 as shown inFIG. 2 for guiding the respiration gas towards the lungs 2 of thesubject, but the gas routing device 30 and the housing assembly 10 isalso in flow communication with the first limb 8 receiving therespiratory gas flow. In this specific embodiment the first limb 8extends to the gas routing device 30 of the arrangement 20 in which casethe first limb is directly connected to the gas routing device. Also inthis specific embodiment the gas routing device is directly connected tothe second limb 9, which means that the gas routing device is betweenthe first limb 8 and the second limb 9. However, it is irrelevantwhether the arrangement or the gas routing device locates in the firstlimb or in the second limb or between these two limbs, but the mainthing is that the arrangement 20 or the gas routing device 30 is in flowcommunication with the breathing circuit or even locates in thebreathing circuit where it can receive the expired gas and guide itthrough the housing assembly 10 and further guide for the inspiration ofthe subject.

The gas routing device 30 is provided with at least two different routeoptions. According to a first route option the expired gas is guidedfirst through the first gas connection 26 or directly to a first port 15of the housing assembly 10, through the housing assembly to the secondport 16 and then discharged from the second port 16 of the housingassembly through the second gas connection 27 or directly to the gasrouting device. According to a second route option the expired gas isguided first through the second gas connection 27 or directly to thesecond port 16 of the housing assembly 10, through the housing assemblyto the first port 15 and discharged from the first port of the housingassembly through the first gas connection 26 or directly to the gasrouting device. So the gas flow through the housing assembly can bearranged in opposite directions. The gas flow guided from the housingassembly 10 to the gas routing device 30 is further guided along thesecond limb 9 for the subject breathing.

In case the housing assembly comprises at least two housings forremoving undesired gas component, the gas flow from the first limb 9 isguided by means of the gas routing device 30 either to the first port 15and through the first housing 17 to the second housing 18 and throughthe second housing to the second port 16 and discharged to the gasrouting device 30 or to the second port 16 and through the secondhousing 18 to the first housing 17 and through the first housing to thefirst port 15 and discharged to the gas routing device 30. The decisionwhether to guide the respiratory gas flow first through the firsthousing 17 or the second housing 18 can be made for instance by a user,

To connect the gas flow between the first housing 17 and the secondhousing 18, which are side by side, there is a connecting channel 23.The connecting channel 23 may be connected to a first intermediate port22 of the first housing 17 and a second intermediate port 24 of thesecond housing 18. The connecting channel 23 is not needed especially incase the first housing and the second housing are one on top of theother. The volume of the connecting channel 23 providing gas flow toboth ways is small to minimize the volume inside the anesthesia machineand to minimize cleaning and service and gas dilution. This connectingchannel can be made out of plastic which could be either reusable andcleanable or disposable. Furthermore, it could be either connected tothe anesthesia machine or completely separate.

The gas routing device 30 in FIG. 2 comprises a body 32 having a firstsector 33 and a second sector 34. Both sectors comprise at least twochannels, the first routing channel 36 and a second routing channel 37,providing the gas flow connection between the housing assembly and thebreathing circuit or its first limb 8 and the second limb 9. Thus thefirst limb 8 can be connected to one of the first gas connection 26 andthe second gas connection 27, and the second limb 9 can be connected tothe remaining one of the first gas connection and the second gasconnection. The first and second gas connections are not necessarilyneeded in case the gas routing device can be connected directly to theports of the housing assembly. In the first sector 33 as shown in FIG. 2the first routing channel 36 is substantially parallel with the secondrouting channel 37, in which case the first routing channel 36 isconnecting the first limb 8 through the first gas connection 26 ordirectly to the first port 15 of the housing assembly 10 and the secondrouting channel 37 is connecting the second limb 9 through the secondgas connection 27 or directly to the second port 16 of the housingassembly 10.

In the second sector 34 the first routing channel 36 and the secondrouting channel 37 are crosswise but passing each other without directflow connection between the first and second routing channel. Thus thefirst routing channel 36 connects the first limb 8 through the secondgas connection 27 or directly to the second port 16 of the housingassembly 10 and the second routing channel 37 connects the second limb 9through the first gas connection 26 or directly to the first port 15 ofthe housing assembly 10.

In FIG. 2 the gas routing device is moving or actually in this specificembodiment sliding or turning from a first position to a second positionso that both the first sector 33 and the second sector 34 can be chosen.In the first position, when the first sector 33 has been chosen, thefirst routing channel 36 of the first sector 33 is connected between thefirst limb 8 and the housing assembly 10 guiding the breathing gas firstthrough the first gas connection 26 or directly to the first port 15 andthrough the housing assembly to the second port 16 and through thesecond gas connection 27 or directly to the second routing channel 37and to the second limb 9 for guiding the breathing gas substantiallyfree from carbon dioxide to the subject. In case there are at least twohousings in the housing assembly the gas flows first through the firsthousing 17 to the first intermediate port 22 and from this port throughthe second intermediate port 24 to the second housing 18 and throughthis second housing to the second port 16.

In the second position, when the second sector 34 has been chosen, thefirst routing channel 36 of the second sector 33 is connected betweenthe first limb 8 and the housing assembly 10 guiding the breathing gasfirst through the second gas connection 27 or directly to the secondport 16 and through the housing assembly to the first port 15 andthrough the first gas connection 26 or directly to the second routingchannel 37 and to the second limb 9 for conveying the breathing gassubstantially free from carbon dioxide to the subject. In case there areat least two housings in the housing assembly the gas flows firstthrough the second housing 18 to the second intermediate port 24 andfrom this port through the first intermediate port 22 to the firsthousing 17 and though this first housing to the first port 15.

As explained hereinbefore the gas routing device 30 can be used tochoose the direction of the respiration gas through the housing assemblyin which case the respiration gas flow direction can be from one of theopposite ports of the housing assembly, which ports are in theembodiment of FIG. 2 the first port 15 and the second port 16. This maybe the fact also in case the housing assembly comprises at least twohousings directing the gas flow through all these housings one after theother irrespective of whether the housings are side by side or one onthe other. The gas routing device of FIG. 2 is manually operated bymeans of a knob 39 for instance by pushing, pulling and turning it.

In practice for instance the first route option is chosen to guide theexpired gas first to the first housing removing the undesired expiredgas component of the respiratory gas flow and after that to the secondhousing removing substantially rest of the undesired expired gascomponent, if such still exists. The second route option may be chosento guide the expired gas first to the second housing removing theundesired expired gas component of the respiratory gas flow and afterthat to the first housing removing substantially rest of the undesiredexpired gas component, if such still exists, but before operating inaccordance with the second option the first housing can be replaced by anew one having more capacity to remove undesired expired gas componentthan with the used first housing. Typically the housing has beenreplaced by the new one, when the capacity of the housing is under apredetermined level just because its capacity has been consumed, whichcan be seen also visually when the color of the substance removing theundesired gas component is changing or the color change is widening tocover the major part of the substance inside the housing.

Another embodiment of an arrangement 20 is shown in more detailed inFIG. 3 for guiding expired respiratory gas flow arrived along the firstlimb 8 through the housing assembly 10. Same reference numbers are usedas in FIG. 2. As a difference compared to the embodiment of FIG. 2, theembodiment of FIG. 3 is electrically operated, but the main principle issame which is to choose the direction of the respiration gas through thehousing assembly 10 in which case the respiration gas flow direction canbe from one of the opposite ports of the housing assembly, which portsare in the embodiment of FIG. 3 the first port 15 and the second port16. This may be the fact also in case the housing assembly comprises atleast two housings directing the gas flow through all these housings oneafter the other irrespective of whether the housings are side by side orone on the other.

The functions of the gas routing device 30 in FIG. 3 are similar to theone introduced in FIG. 2, but this gas routing device is electricallyoperated by means of a control unit 41. The arrangement 20 in FIG. 3also comprises sensors, such as a first sensor 42 and a second sensor 43in case of two housings in the housing assembly 10, The more sensors maybe needed the more housings are needed. The first housing 17 may beprovided with the first sensor 42 and the second housing 18 may beprovided with the second sensor 43. The sensors may be signaling apresence of the housings and which housing is a newer one consideringthe removing capacity of undesired gas component. Also this signal canbe used to choose the respiratory gas flow direction through the housingassembly, whether it is guided first through the first housing or thesecond housing. As explained hereinbefore the gas flow is advantageouslyguided first through the housing, which is the used one and whichtypically also includes partly the substance, which is unable to removeor absorb the undesired gas component from the gas flow, which thusincludes less the active substance removing undesired gas component fromthe respiratory gas than the new housing with new active substance.After that housing the gas flow is guided through the new housingincluding substance having substantially full capacity to remove theundesired gas component from the gas flow.

The signal from the first and second sensors is received by the controlunit 41, but shown to the user by means of an indicator 44, such as ledchange indicator. The signal may indicate to the user the direction ofthe respiratory gas flow through the housing assembly 10 and which oneof the first housing 17 and the second housing 18 should first bechanged to a new one, when it is time to do that due to the fact thatthe capacity to remove undesired gas component like carbon dioxide isinsufficient.

Also the arrangement can be provided with a change controller (not shownin Figure) to control that only the housing that is upstream to the flowis available to be replaced and prevent to change the housing which isdownstream. In other words the housing which receives first therespiratory gas flow is replaced first, but another housing receivingthe gas flow after that is left unchanged. When the new housing hasreplaced the used one, the flow direction is changed opposite to guidethe flow from the housing unchanged to consume its absorbing capacityfirst and then direct the flow to the new one. This may be advisable toget the full capacity out from an absorber material inside the housingand to avoid replacing such housing which has still a lot of capacityleft, but to replace the housing that is exposed to the CO2 gas first.The downstream/upstream position of the housings may be changed bychanging the flow direction by means of the gas routing device 30 of thearrangement 20, to avoid by physically changing the housings in respectto each other.

The embodiments described above solve the problem due to inability tofully exploit the capacity to remove the undesired gas component in thehousing assembly. Also, when using one of two housings to return thebreathing gas to the breathing circuit, cleaning of the bigger amount ofparts needed in well-known designs for the gas return to the breathingcircuit can be avoided which is an advantage. As well an increased totalvolume of the housing assembly can be solved by the housing assemblyhaving at least two housings where one of the housings in itselfprovides a part of the gas return conduit. That is anintegrated/inherent gas return conduit to minimize the volume inside theanesthesia machine requiring cleaning and service and diluting gases.

Also, the advantage of the embodiments is the use of both two andmultiple housings as well as a single integrated housing design forthose users who value more decreased maneuvering needs over increasedabsorbent use rate.

Typically the housings could be swapped and replaced with apredetermined order. This may be advantageous because in order to getthe full capacity out from the housing with the undesired gas componentremoving substance it needs to be the housing that is exposed to the CO2gas first. If it was the other way around a premature CO2 breakthroughwould happen inhibiting the full usage of the capacity of the housing.With embodiments show in FIGS. 2 and 3 the user does not need to swaparound the housings already in use but only replace the one that is usedup. The downstream/upstream position of the units is changed by changingthe flow direction, not by physically changing the units in respect toeach other.

The written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claim.

What is claimed is:
 1. A system for guiding expired respiratory gas flowin a breathing circuit, the system comprising: a plurality of housingsin serial flow communication; and a gas routing device coupled to afirst of the plurality of housings and a last of the plurality ofhousings, the gas routing device configurable between at least two routeoptions; wherein for a first of the at least two route options, the gasrouting device is configured to guide the expired respiratory gas flowthrough the plurality of housings from the first of the plurality ofhousings to the last of the plurality of housings, and wherein for asecond of the at least two route options, the gas routing device isconfigured to guide the expired respiratory gas flow through theplurality of housings from the last of the plurality of housings to thefirst of the plurality of housings.
 2. The system of claim 1, furthercomprising a plurality of sensors corresponding to the plurality ofhousings, the plurality of sensors configured to signal a respectivepresence of the corresponding plurality of housings.
 3. The system ofclaim 2, wherein the plurality of sensors are configured to indicate arespective capacity of the plurality of housings to remove expired gascomponent from the expired respiratory gas flow.
 4. The system of claim3, further comprising a controller configured to electrically operatethe gas routing device based on signals from the plurality of sensors.5. The system of claim 1, further comprising a change controllerconfigured to control an availability of the plurality of housings to bereplaced.
 6. The system of claim 5, wherein the availability to bereplaced is based on a housing of the plurality of housings that isupstream to the expired respiratory gas flow.
 7. The system of claim 1,wherein the gas routing device comprises a first sector corresponding tothe first of the at least two route options and a second sectorcorresponding to the second of the at least two route options.
 8. Thesystem of claim 1, further comprising a first limb for receiving theexpired respiratory gas flow and a second limb for discharging theexpired respiratory gas flow.
 9. The system of claim 8, wherein for thefirst of the at least two route options, the first limb is in flowcommunication with the first of the plurality of housings and the secondlimb is in flow communication with the last of the plurality ofhousings.
 10. The system of claim 8, wherein for the second of the atleast two route options, the first limb is in flow communication withthe last of the plurality of housings and the second limb is in flowcommunication with the first of the plurality of housings.
 11. A systemfor guiding expired respiratory gas flow in a breathing circuit, thesystem comprising: a first housing having a first port and a firstintermediate port; a second housing having a second port and a secondintermediate port, the first intermediate port coupled to the secondintermediate port; and a gas routing device coupled to the first portand the second port, wherein the gas routing device is configurablebetween a first route option from the first port to the second port, anda second route option from the second port to the first port.
 12. Thesystem of claim 11, further comprising a first sensor configured tosignal a presence of the first housing and a second sensor configured tosignal a presence of the second housing.
 13. The system of claim 12,wherein the first sensor is configured to indicate a capacity of thefirst housing to remove expired gas component from the expiredrespiratory gas flow and the second sensor is configured to indicate acapacity of the second housing to remove the expired gas component fromthe expired respiratory gas flow.
 14. The system of claim 13, furthercomprising a controller configured to electrically operate the gasrouting device based on signals from the first and second sensors. 15.The system of claim 11, further comprising a change controllerconfigured to control an availability of the first and second housingsto be replaced.
 16. The system of claim 15, wherein the availability tobe replaced is based on a housing of the first and second housings thatis upstream to the expired respiratory gas flow.
 17. A system forguiding expired respiratory gas flow in a breathing circuit, the systemcomprising: a first housing having a first port and a first intermediateport; a second housing having a second port and a second intermediateport, the first intermediate port coupled to the second intermediateport; and a gas routing device comprising: a first sector comprising afirst routing channel and a second routing channel; a second sectorcomprising a third routing channel and a fourth routing channel, whereinthe gas routing device is configurable between a first route optioncorresponding to the first sector and a second route optioncorresponding to the second sector, wherein for the first route optionthe first routing channel is coupled to the first port and the secondrouting channel is coupled to the second port, and wherein for thesecond route option the third routing channel is coupled to the secondport and the fourth routing channel is coupled to the first port. 18.The system of claim 17, further comprising a first sensor configured toindicate a capacity of the first housing to remove expired gas componentfrom the expired respiratory gas flow and a second sensor configured toindicate a capacity of the second housing to remove the expired gascomponent from the expired respiratory gas flow.
 19. The system of claim18, further comprising a controller configured to electrically operateselection of the first route option or the second route option based onsignals from the first and second sensors.
 20. The system of claim 17,further comprising a change controller configured to control anavailability of the first and second housings to be replaced based on ahousing of the first and second housings that is upstream to the expiredrespiratory gas flow.